Si:WO3 heterostructure for Z-scheme water splitting: an ab initio study

Abstract

The Si:WO₃ heterostructure is expected to have suitable band alignment for the Z-scheme water splitting, but the heterostructure interfaces have been scarcely studied. In this work, a series of interfaces between the WO₃ (100) and Si (001) surfaces, which have a small lattice-mismatch, are studied using ab initio calculations. When there is no atom diffusion across the interface, a Si–O bonded interface with Si dimers is the most stable. Analysis of the electronic structure shows that the interfacial Si and O atoms are fully saturated, leading to a clean interface without localized gap states. O diffusion from WO₃ into Si is found to be thermodynamically possible, but it does not affect the full bond saturation of the interfacial atoms. A type-II band alignment exists between Si and WO₃, with the WO₃ conduction band about 0.5 eV higher than the Si valence band, which is not influenced by O diffusion. A band diagram is plotted for the Si:WO₃ heterostructure to evaluate its photocatalytic capability, and the influence of the small Schottky barrier and the interface amorphous layer is discussed.